This invention relates to a method of manufacturing an in-the-ear hearing aid which is worn in the auditory canal of a user in the proximity of his or her tympanic membrane. The hearing aid comprises a first part which, when the hearing aid is present in the auditory canal, is situated near the tympanic membrane in a first part of the auditory canal. This first part of the auditory canal has a substantially non-deformable wall. The hearing aid comprises a second part which, when the hearing aid is present in the auditory canal, is situated near an auricle in a second part of the auditory canal. The second part of the auditory canal has an elastic wall. In this method, first a mold of the auditory canal is made, then a housing for the hearing aid is made, the mold being used as a template, and subsequently components are mounted in the housing. The auditory canal is filled with a viscous material in order to make a mold of the auditory canal and the mold is removed from the auditory canal after solidification of said material.
A method of the type defined in the opening paragraph is described in the non-prepublished European Patent Application No. 92202781.8, which corresponds to U.S. application Ser. No. 943,366 filed Sep. 10, 1992. This method makes it possible to manufacture an in-the-ear hearing aid which precisely fits the auditory canal of a user. However, in order to be worn conveniently it is desirable that the hearing aid fits rather tightly in the auditory canal. Since the wall of the first part of the auditory canal is substantially non-elastic and the auditory canal is very sensitive at this location, the hearing aid cannot be fitted tightly in this part of the auditory canal. For this purpose the shape of the heating aid should be such that when present in the auditory canal the hearing aid causes a slight elastic deformation of the wall of the auditory canal. In order to determine the shape of the auditory canal in the deformed condition it is customary to make a further mold of the second part of the auditory canal, a paste-like substance being introduced into the auditory canal under pressure in a manner such that the wall of the auditory canal is deformed. This method does not allow a mold of the entire auditory canal to be made because the first part of the auditory canal is too sensitive to permit the paste-like substance to be applied under pressure. After the two molds have been made the two molds are cut to length and joined to one another. Joining is difficult because the exact shape of the transitional area between the first and the second part of the auditory canal, the second part being expanded, is not known.